1) Field
These embodiments relate to electric actuators and more specifically to the construction of their current-carrying portions.
2) Discussion of Related Art
Electric actuators are often used in, for example, automobiles to actuate seats, mirrors, and windshield wipers. Electric motors, such as those found in the aforementioned automobile components, and voicecoil actuators, such as those found in speakers, are typical forms of an electric actuator. Other forms of electric actuators include linear motors, such as those used in the machine tool industry.
Disadvantageously, electric actuators usually require a form of transmission attached to their output to multiply the torque or force they produce in order to meet the force or torque requirements of the application. For example, a cordless drill is driven by a small DC (direct current) electric motor, a form of electric actuator, that is attached to a transmission typically comprised of multiple stages of gear reduction. A transmission typically trades speed for torque; that is, a motor producing motion at its output shaft that is high speed and low torque is fed into a transmission that results in motion that is at low speed and high torque at the output. There are many forms a transmission can take, from something as simple as a pivoting linkage that has a load attached at one point and the electric actuator at another, to a complex continuously variable transmission of the type that some automobiles are produced with today. Transmissions add sources of failure, increase the cost of the system, and reduce system efficiency. It is not uncommon, for example, to lose several percent of the power going through a transmission, primarily as a result of friction. Transmissions also typically add other unwanted problems. Gear transmissions usually add backlash, which is mechanical play between meshing gear teeth. When precision control of a system is attempted, such as in a robotic or machine tool application, this mechanical play can cause a great deal of problems. For such reasons, various attempts have been made to increase the force or torque for a given size of an electric actuator, especially electric motors (because these are the most common form of electric actuator). By increasing the torque of an electric motor, for example, a designer can use a smaller transmission ratio (the ratio of input motion to output motion) or no transmission at all. A smaller required transmission ratio typically results in a smaller, cheaper transmission that has lower backlash, and having no transmission at all is even better. Therefore, it is a primary objective of electric actuator designers to increase torque for a given motor size. For example, U.S. Pat. No. 6,864,613 to Graham, et al. shows windings of an electric motor with a higher conductor packing density than is typical, but the gains in torque for a given size of windings and input current are modest because the gain in actual copper to the windings through the reduction of insulation is small. U.S. Pat. No. 5,396,140 to Goldie, et al. and patent application Ser. No. 09/770,939 to Wittig both show motors that have multiple sets of windings sharing a single magnetic return path, which may increase the torque over a motor with a single set of windings by the number of rotors present. Again, the torque gains for such a design for a given motor size may not be significantly increased.
It is therefore an objective of the present embodiments to present an electric actuator that may have significantly increased force or torque for a given actuator size.